The present invention relates to a storage/transport container for radioactive material. More particularly this invention concerns such a container and a method of making it.
A storage/transport container for spent nuclear-fuel rods or the like is typically formed like a barrel and has inner and outer spaced shells forming a cylindrical intermediate space. The chamber is filled with aggregate and a suspension of cement, water, and additives to form a concrete mass. The aggregate which is used to impart strength to the container has a minimum particle size.
In a known method described in WO 98/59346 the entire space between the shells is filled with the same concrete mix. Containers made in this way are suitable only for shielding radiation sources having relatively low neutron source strength, for example low-burn-out fuel elements. If a container of this kind is to be used for radiation sources with high-dosage neutron source strength, e.g. MOX fuel elements or vitrified highly active waste from reprocessing, relatively thick concrete walls are required to hold the water needed for the neutron shielding.
It is therefore an object of the present invention to provide an improved a storage/transport container for radioactive waste materials.
Another object is the provision of an improved method of making a storage/transport container for radioactive waste materials which overcomes the above-given disadvantages, that is which can produce a container with adequate n-shielding without having to resort to large wall thicknesses or complex manufacturing methods.
A storage/transport container for radioactive material is made according to the invention by first subdividing a chamber formed between an inner shell and an outer shell into first and second compartments by means of a foraminous partition having a predetermined maximum mesh size. Then an aggregate of a predetermined minimum particle size greater than the predetermined maximum mesh size is introduced into one of the compartments and a suspension of cement and water is introduced into either of the compartments such that the aggregate remains in the one compartment and the cement and water flow through the partition to fill both compartments. Normally according to the invention the aggregate and the suspension are both introduced into the same compartment.
With this arrangement, therefore, the aggregate will be restricted to the one compartment it is introduced into while the grout-like suspension will fill the other compartment. This forms standard concrete with the aggregate to produce the requisite container strength while providing a layer with a high water content for best n-shielding.
The partition according to the invention is formed by a perforated screen, plate, or netting. Its mesh size is between 2 mm and 4 mm.
The partition is supported between the shells on webs bridging the chamber and bearing on the shells. More particularly the partition can be supported between the shells on an inner array of inner webs and an outer array of outer webs. in this case the partition is shaped to fit complementarily with the inner and outer webs. The inner and outer webs are arrayed in pairs interconnected by respective inner and outer bridges secured to the respective shells. The partition can be welded to the webs.
As mentioned above, the one compartment is the second compartment so that the aggregate and cement/water suspension are introduced into the same compartment. More particularly the one and second compartment are an inner compartment adjacent the inner shell. The other and first compartment is an outer compartment adjacent the outer shell.